In an Evolved Packet System, radio base stations (eNodeBs) are connected to Mobility Management Entities (MMEs), for control of mobile User Equipment (UE) in the network. One eNobeB may be connected to one or more MMEs. To find a UE in the network for e.g. an incoming message, the MMEs asks the eNodeBs to send paging messages in the cells. As an example, two geographically separated MMEs serving areas consisting of several tracking areas (TAs) page the UE only in one or more tracking areas where it is currently registered, to lower the paging load in the network. To enable communication between the eNodeB and the MME an S1 Application Protocol (S1-AP) signalling connection need to be setup, which is performed according to an 51 setup procedure. The S1 Setup procedure is defined in 3GPP TS 36.413 and by means of this procedure the ENodeB sets up an S1-AP signalling connection to the MME. S1-AP is an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) radio network layer signalling protocol for the S1 interface.
The S1 interface is the interface between the radio base station in the E-UTRAN and the MME in the Evolved Packet Core Network of the Evolved Packet System. The radio base stations in the E-UTRAN may communicate with one another over an X2 interface.
Different areas in the radio communications network may be served by different MMEs and the cell or cells of an eNodeB are configured with a Tracking Area Code (TAC). During the S1 Setup procedure the eNodeB includes all its broadcast TACs in an S1 Setup Request message to the MME, when initiating the S1-AP signalling connection to the MME. The S1 Setup Request message includes detected TACs. The MME has no possibility to reject certain broadcast TACs that are not served by this MME, but only to reject or accept the S1 Setup procedure as a whole. This allows the configured cells of a certain eNodeB only to be from the same geographical pool area, a singular pool area configuration and makes the cell configuration non flexible and requires signalling between MMEs.